A number of methods are available in the prior art for bonding metal bodies to ceramic bodies. One example of such methods includes the use of a brazing method in which a preform of suitable active brazing metals are placed between the ceramic and metal bodies. The preform is thin, on the order of about six mils, and is applied to the ceramic body joint surface having an area which is larger in extent to the metal body joint surface to be bonded thereto. The two joint surfaces are of substantially identical curvature. One of problems of the prior art methods is the brazing metals do not wet the entire joint bonding surface of the ceramic body so that any thermal mismatch stress between the metal and the ceramic bodies can be distributed across the entire ceramic body joint surface. This problem can be due to too fast a heating cycle which results in the temperature of the metal body rising more rapidly than the temperature of the ceramic body. Another problem associated with the use of a preform brazing alloy is brazing a metal body to an inverted ceramic body bonding surface such as the lower end surfaces of the ceramic body. In such instances, the preform will sag away from the ceramic body as the preform melts resulting in non-uniform and substantially weaker brazing fillets.
U.S. Pat. No. 4,917,642 discloses various methods of bonding metal cover members to ceramic tubular members via brazing. One method comprises preparing a mixture of an active metal powder such as Ti and/or Zr, an organic binder such as polyvinyl alcohol and ethyl cellulose and a solvent such as ethanol and tetralin and applying the mixture on the bonding surface of the ceramic tubular member through a metal mesh screen and the like. An Ag-brazing filler metal preform or foil is placed on the ceramic member's joint bonding surface coated with the active metal. The metal cover member is then placed onto the brazing filler metal foil before the resulting ceramic to metal assembly is heated and cooled to form the desired bond. This prior art method has the disadvantages noted above in the use of a brazing preform.